1. Field of the Invention
The present invention relates to an FET band amplifier used in various receivers and so on.
2. Description of the Related Art
Band amplifiers that amplify signals of a predetermined band in high gain are used in various kinds of receivers such as an AM receiver and an FM receiver. Typical band amplifiers include a high-frequency amplifier included in a front end and an intermediate frequency amplifier that amplifies intermediate frequency signals. In the high-frequency amplifier, only signals of in a predetermined band centering around a tuning frequency are selectively amplified. The center frequency in this case is set to be variable depending on the state of channel selection. In the intermediate frequency amplifier, only signals of a narrow band close to the intermediate frequency are selectively amplified. The center frequency in this case is set to a fixed value such that for example, the center frequency is 10.7 MHz in the case of the FM receiver, and the center frequency is 455 kHz in the case of the AM receiver. Generally, a multistage amplifier with transistors connected in multiple stages is used in case where a high gain is set in the band amplifier.
Incidentally, the band amplifier described above has a problem such that if a high gain is set, the multistage amplifier may be saturated with the noise component, thus making it impossible to obtain a gain realizable in design.